Development of Oil-Based Polyol

Development of Oil-Based Polyols and Application to Polyurethane Formulation  

Introduction

Petroleum derivatives constitute an important portion of the raw materials for plastics used in our daily lives. Due to the harmful effects of petroleum derivatives on the environment and the depletion of petroleum resources, the synthesis and use of bio-based materials is one of the important research areas today. At its 2002 meeting in Johannesburg, the UN reached consensus on the use of biological resources.[1] Throughout history and today, animal and plant oils represent the most important renewable resources for the chemical industry. For example, oils have long been used in soap production as a result of transesterification reactions. Additionally, oil-based alcohols obtained from the hydrogenation of fatty acids and oil methyl esters are used in surfactant production. Recently, significant developments have been made in plant-derived polymers. Examples include thermoset resins derived from soybean oil, biodegradable polymers, biocomposites, and polyurethane dispersions. When obtaining polymers from oils, the oils (or fatty acids) must first be converted into monomers that polymerize well. Within this scope, extensive research has been conducted on polymers of epoxidized soybean oil with polyamines or polyols, and on the use of castor oil containing hydroxyl functional groups in its molecule as a monomer in polyurethane synthesis. The production of rigid plastics from oils gained importance particularly after the 1970s. The ability to produce oil-based resins, at least in part, from a natural agricultural product provides a significant contribution both socially and economically. The developments observed in work aimed at the production of polymer-based materials and the modification of their properties are expected to increase further in the coming years. In this study, polyol was obtained from soybean oil and used in a polyurethane foam formulation.

1. The Importance of Renewable Resources

Polymers are widely used due to their diverse functions, light weight, low cost, and chemical stability.[2] As the world population increases, demand for these materials also increases. Therefore, solutions must be found to meet these demands. Petroleum derivatives are used as raw materials in the production of a significant portion of the polymers used in our daily lives. As a result of the harmful effects of petroleum derivatives on the environment and the depletion of petroleum resources, the synthesis and use of bio-based materials are increasing. It is estimated that approximately 400,000 barrels of oil are used daily in plastic material production for global supply. Plastic materials generally cause environmental pollution because they persist in nature for extended periods. For example, polyethylene-based plastic bags completely decompose in nature at least 200 years after being discarded. Similarly, PET bottles require at least 400 years to completely break down in nature. Petroleum-based plastic remaining in soil for long periods releases toxic and harmful chemicals during decomposition. Over time, these plastic wastes are digested by organisms and decomposers living in the soil. In this case, living organisms in the soil are also exposed to the same negative effects and disappear, causing disruption to soil balance and even water balance. As a result of excessive use of petroleum-based plastic products, plastic waste continues to accumulate in the environment and can have serious consequences for the ecosystem.[3] According to research, approximately 6.3 billion tons of plastic were produced globally between 1950 and 2018, with only 9% recycled and 12% incinerated.[4] Important work is being conducted to resolve the waste problem of petroleum-based plastics. The most important of these efforts is recovery facilities. Within the framework of environmental awareness, the widespread adoption of recycling is seen as an important solution to the waste problem. As an emergency measure, work on the production and use of bioplastics is also increasing. As petroleum resources proved insufficient to meet demand, new alternative raw materials and production technologies gained importance. The first oil crisis in 1973 affected the world demand and importance of raw materials derived from petroleum reserves.[5] Figure 1 shows past and projected global oil production.[6] [caption id="attachment_144799" align="aligncenter"] Figure 1: Past and projected global oil production [6][/caption] Since petroleum resources are depleted daily and are not renewable, petroleum-based raw material prices are expected to increase further. As a result of these realities, public demands are driving researchers to develop more economical alternative raw materials.

2. Renewable Resources

2.1 Plant Oils

Plant oils have been used as alternative raw materials in the chemical sector for many years. Plant oils are attractive candidates among other renewable resources due to their widespread availability, low cost, low toxicity, biodegradability, and ease of chemical modification.[7] Additionally, the long fatty acid chains of plant oils provide flexibility and toughness to the product. Plant oils consist essentially of triacylglycerols, which are the result of esterification of glycerol with three fatty acids. Fatty acids constitute 95% of the total weight of triglycerides, and their content varies depending on the plant oil.[8]

2.2 Soybean Oil

The soybean is an oilseed plant with high oil and protein content. As shown in Figure 2, oil constitutes 19% of the chemical composition of the soybean, while crude protein constitutes 36%.[9] The soybean plant can be adapted to various climate zones. It is successfully cultivated in many regions of the world. Approximately 32% of soybean oil is produced in the United States, 17% in Brazil, 13.5% in China, 12% in Argentina, 11% in the European Union, and 3% in India and Japan.[10] [caption id="attachment_144800" align="aligncenter"] Figure 2: Chemical composition of soybean [9][/caption] Soybean oil is refined using various methods, the most common being solvent extraction. Additionally, soybean oil consists of a combination of unsaturated oleic and linoleic and linolenic glycerol esters with saturated palmitic and stearic acids. Soybean oil is one of the most preferred chemically renewable raw materials. The reasons for this are its ability to be produced in large quantities, easy availability, and high unsaturation. However, despite this high unsaturation, these double bonds are not very reactive, so functionalization must be carried out before they can be used as monomers in polymerization reactions.[11]

3. Oil-Based Polyurethanes

Petroleum-based polyols derived from petroleum raw materials are predominantly used in polyurethane production. However, the negative effects on the environment and the depletion of petroleum reserves have encouraged the development of polyurethanes from bio-based and renewable raw materials. Plant oil-based polyols are a good alternative to petroleum-based polyols. Bio-based polyols are currently being commercialized by companies such as Dow Chemical, Bayer Material Science, BASF SE, and Shell Chemicals Ltd. Additionally, plant oil-based polyols and polyurethane systems derived from them are a quite popular research topic in the academic field. Castor oil, epoxidized soybean oil, and soybean oil with acrylic acid functional group additives hold an important place in obtaining polymers from oils because they contain natural hydroxyl groups. The objective of our project work was to develop soybean oil-based polyols applicable in the polyurethane industry. Within the scope of the project, as seen in Figure 3, a polyol was synthesized from soybean oil using epoxidized soybean oil with diethanolamine and ZnCl2 catalyst. [caption id="attachment_144801" align="aligncenter"] Figure 3: Structure of the polyol synthesized within the scope of the project (Other fatty acids in the triglyceride are not shown for better visualization of the figure)[/caption] The synthesized polyols were used at Flokser Kimya San. ve Tic. A.Ş. in rigid polyurethane foam formulations deemed appropriate according to their hydroxyl numbers. Additionally, the mechanical properties, densities, and thermal conductivities of the obtained foams were examined. Rigid polyurethane foams were obtained through the reaction between Polyol I synthesized using soybean oil and PMDI (Figure 4). To obtain the polyurethane foam, a mixture was prepared using Polyol I in different proportions along with an appropriate catalyst, blowing agent, water, silicone, polyether polyol, and flame retardant. [caption id="attachment_144802" align="aligncenter"] Figure 4: Rigid polyurethane foam obtained using Polyol I[/caption] The prepared mixture was mixed with PMDI at 21°C. Special attention was paid to ensuring that both the mixture and PMDI were at this temperature. After the mixing operation was performed with a mechanical mixer, the foam was cast by hand. During foam formation, reaction profiles (cream time, gel time, and tack-free time) were measured as shown in Table 1. In the table, while the cream time, gel time, and tack-free time of the polyurethane foam prepared with standard polyether polyol were 7s, 28s, and 36s respectively, these times were measured as 5.4s, 15.8s, and 19.9s respectively in the formulation containing 50% Polyol I. As the amount of Polyol I in the formulation increased, the reaction profiles of the foams decreased. [caption id="attachment_144803" align="aligncenter"] Table 1: Reaction profiles of polyurethane foams[/caption] Polyol I was added to the polyurethane formulation at mass percentages of 5%, 15%, 25%, 50%, 75%, and 100% according to the polyol blend ratio. Following the reaction profiles, the densities and curing of foams prepared with standard polyether polyol were compared with foams containing Polyol I. As seen in Table 2, as the proportion of Polyol I in the formulation increased, the densities of the foams decreased. For example, while the density of the foam prepared with standard polyether polyol was 31 kg/m³, the density of the foam containing 100% Polyol I was found to be 25.8 kg/m³. A decrease in density can be achieved by adding water to the polyurethane foam formulation. The reduction in density here is thought to be caused by trace amounts of moisture remaining in Polyol I. [caption id="attachment_144804" align="aligncenter"] Table 2: Free density of polyurethane foams[/caption] Table 3 contains the results of the cure test. The cure test is a method in which pressure is applied to the foam using a device called Instron at 3.5, 5, and 8 minutes after foam formation to measure the rate of curing. As seen, increasing the amount of Polyol I increased curing. For example, while the cure values of the standard foam at 3.5, 5, and 8 minutes were 87.4, 107.5, and 167.8 kPa respectively, for the foam containing 100% Polyol I, these values were found to be 119, 135, and 155.5 kPa respectively. [caption id="attachment_144805" align="aligncenter"] Table 3: Cure test results of polyurethane foams[/caption] Additionally, the compressive strength and thermal conductivity of foam produced using standard polyether polyol were compared with foam containing only 100% Polyol I. Table 4 contains the compressive strength and thermal conductivity results. The results show that when 100% Polyol I is used in the foam formulation, there is a decrease in both compressive strength and thermal conductivity. [caption id="attachment_144806" align="aligncenter"] Table 4: Compressive strength and thermal conductivity results for foam containing 100% Polyol I and foam with standard polyether polyol[/caption] Compressive strength was performed according to ISO 844 standard (ISO 844, 2021). Force was applied to the foam placed in the Instron device, and compressive strength was measured when 10% compression was reached. Figure 5 shows the compressive strength graph versus relative deformation resulting from the compressive strength test. Curve a in the graph belongs to the standard foam, while curve b belongs to the foam containing 100% Polyol I. As seen, while the compressive strength for the standard foam was 127 kPa, it decreased to 106 kPa when 100% Polyol I was used. [caption id="attachment_144807" align="aligncenter"] Figure 5: Compressive strength graph of polyurethane foams a) Standard polyether polyol foam without Polyol I, b) Foam containing 100% Polyol I[/caption] The biodegradation process of the obtained foams is monitored at regular intervals after being placed in soil by tracking weight and appearance changes. (Figure 6) [caption id="attachment_144808" align="aligncenter"] Figure 6: Changes in foams occurring within a 1-month period in the biodegradation study.[/caption]

Conclusion

Plastics will continue to be used in our daily lives. Developed countries have attached importance to and supported the development of projects related to the recovery of plastic waste in order to solve raw material and environmental problems. In addition to the widespread adoption of recovery facilities, work on the use of biodegradable plastics is seen to be conducted in parallel. Problems encountered in separating plastic derivatives from each other and certain levels of impurities remaining during recovery affect the thermo-mechanical values of the product resulting from the process. Additionally, new regulations show increased pressure on the use of natural raw materials. Our work demonstrates that soybean oil-based polyurethane foams can be successfully synthesized and that the mechanical properties of the products show commercially viable product characteristics when compared with standard polyurethane foam. Furthermore, since the products are bio-based polyol materials, it is anticipated that biodegradability will be achieved in a shorter timeframe, and work in this area is ongoing.

Acknowledgements

We thank Flokser Kimya San. ve Tic. A.Ş. for the polyurethane foam formulation. We thank TUBITAK for supporting our project work (project application no: 1139B412100207).   References [1] United Nations, Report of the World Summit on Sustainable Development Johannesburg, South Africa, August 26-September 4, 2002.http://www.un.org/esa/sustdev. [2] Huang, C., Qian, X., & Yang, R. (2018). Thermal conductivity of polymers and polymer nanocomposites. Materials Science and Engineering: R: Reports, 132, 1-22. [3] Tan, S. X., Andriyana, A., Ong, H. C., Lim, S., Pang, Y. L., & Ngoh, G. C. (2022). A Comprehensive Review on the Emerging Roles of Nanofillers and Plasticizers towards Sustainable Starch-Based Bioplastic Fabrication. Polymers, 14(4), 664. [4] Alabi, O. A., Ologbonjaye, K. I., Awosolu, O., & Alalade, O. E. (2019). Public and environmental health effects of plastic wastes disposal: a review. J Toxicol Risk Assess, 5(021), 1-13. [5] Azapagic, A., Emsley, A., & Hamerton, I. (2003). Polymers: the environment and sustainable development. John Wiley and Sons. KİTSP [6] The Hubbert Curve for the Whole Earth, https://planetforlife.com/ oilcrisis/oilpeak.html (28.03.2022). [7] Liu, F., & Zhu, J. (2014). Plant-oil-based Polymeric Materials and their Applications. Green Materials from Plant Oils, 29, 93. [8] de Espinosa, L. M., & Meier, M. A. (2011). Plant oils: The perfect renewable resource for polymer science?!. European Polymer Journal, 47(5), 837-852. [9] Purdue University Agricultural & Biological Engineering, Parts of the soybean that may be used for competition products, https://engineering.purdue.edu/ABE/academics/competitions/soybean_part (28.03.2022) [10] The Market Prices of Soya (2017) https://www.flickr.com/photos/unitedsoybean/22566265820 (28.03.2022). [11] Dasari, M. A. (2003). Reaction Engineering Options for Producing Biodiesel and Cetane Improvers from Fats and Oils (Doctoral dissertation, University of MissouriColumbia).   Prof. Dr. Tarık Eren Department of Chemistry Yıldız Teknik Üniversitesi   Elmas Kırtay Undergraduate Student Department of Chemistry Yıldız Teknik Üniversitesi   L. Yusuf Yivlik Research and Development Manager Flokser Kimya